1. Field of the Invention
The present invention is related to a non-volatile static random access memory (NVSRAM) device, and more particularly, to an NVSRAM device using an inverter circuit and a non-volatile erasable programmable memory (NVEPM) circuit for providing data backup.
2. Description of the Prior Art
There are essentially two types of data memory devices used in computers today, “non-volatile” and “volatile” memory devices. Common non-volatile memory devices include well-known read only memory (ROM) devices, such as EPROM (erasable programmable ROM) devices, EEPROM (electrically erasable programmable ROM) devices or flash ROM devices. The name “non-volatile” comes from the fact that these non-volatile memory devices maintain the data stored therein, even when power to the device is removed or temporally lost. Volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM) devices. RAM devices have been widely used for temporary data storage, such as during data manipulation, since writing data into or reading data out of these devices can be performed quickly and easily. However, a disadvantage of these volatile devices is that they require the constant application of power, such as in the form of a data refresh signal, to refresh and maintain data stored in the memory cells of the chip. Once power supplied to the device is interrupted, the data stored in the memory cells of the chip is lost.
When used in a computer system, non-volatile memory devices suffer from endurance problem caused by repeated cycling program/erase operations, as well as slow the speed of the computer system due to longer programming time. On the other hand, SRAM with fast data access speed and long lifetime is suitable for use in the computer system, such as in BIOS. However, since SRAM is a volatile memory device, the stored data stored will be lost if power is interrupted. Therefore, computer system designers have recognized the need to back up information stored in non-volatile memories in the event of power failure.